The present invention relates to an apparatus, method and system for tracking a medical instrument in three-dimensional (3-D) space based on diagnostic scan data and intra-operative stereo images. The invention has particular application in tracking instruments, both flexible and rigid, as they are moved inside a patient""s body. The invention also relates to a processor-readable medium embodying a program of instructions (e.g., software) which may be employed with the apparatus or system for implementing aspects of the tracking method.
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Various scanning techniques are known for imaging and mapping body structures, which provide information regarding the location of a target site in a patient""s body for surgical or diagnostic procedures. One such technique employs still photography, videography, radiological x-rays, or angiography to produce a 2-D projection of a 3-D object.
Another technique involves (1) acquiring 2-D image scans of the operating space and internal anatomical structures of interest either pre- or intra-operatively; (2) reconstructing 3-D images based on the acquired 2-D scans; and (3) segmenting the 3-D images. The scans are typically computerized tomographic (CT) scans, positron emission tomography (PET) scans, or magnetic resonance image (MRI) scans.
The image scans are registered with the patient to provide a basis for localizing or tracking a medical instrument with respect to anatomical features or other elements in the images, as the instrument is moved within the operating field during surgery. Registration involves the point-for-point mapping of the image space to the patient space, allowing corresponding points to be mapped together. Corresponding points are those points that represent the same anatomical features in two spaces.
With registration established, appropriate equipment can be used to track the medical instrument relative to internal structures of the patient as it is navigated in and around the patient target site during surgery. Images of the target site are displayed to assist the user (e.g., the surgeon) in navigating to the target site. Conventional tracking equipment includes a structure to define a 3-D reference coordinate system relative to the patient or operating space.
One such structure used for instrument localization or tracking in neurosurgery is a large ring-like device which surrounds the patient""s head and is fixed relative thereto. The ring establishes a 3-D coordinate system with respect to the patient""s head. A separate calibration unit having an array of rod elements is fixed to the ring to surround the head during the generation of scan and/or 2-D images. The rods, which have known coordinates in the 3-D coordinate system defined by the ring, produce spots in the scans. Other features in the volume scans can then be assigned coordinates in the 3-D coordinate system by correlation with the known coordinates of the spots produced by the rod elements.
After the images are made, the calibration unit is detached from the ring, and a guidance arc calibrated to the 3-D coordinate system of the ring is attached in its place. The arc provides coordinate reference information to guide the instrument which is usually attached to the arc.
Cranial implants of radio-opaque or MRI-opaque materials have also been used as a localization structure. Three or more of such implants are made and used to establish a 3-D coordinate system.
Another type of localization device is a fiducial structure which is positioned in the operating space for calibrating the operating space in terms of a 3-D coordinate framework. The fiducial structure includes a set of fiducial points connected by a frame constructed to hold the points in fixed spatial relation to each other. The 3-D operating space framework is derived by computation from two 2-D projections of a calibration image pair obtain from video cameras made with the fiducial structure positioned in the operating space. After the calibration image pair is made the fiducial structure is removed, and a standard projection algorithm is used to reconstruct the operating space framework from the calibration image pair. Such framework is then aligned with a 3-D volume scan framework and can be used to locate and track a medical instrument in the operating space, so long as the cameras remain in fixed positions relative to the operating space.
A basic disadvantage with these conventional 3-D reference frame structures is that they add an extra degree of complication to the tracking process by establishing a coordinate framework for the operating space.
In the area of computer-assisted spine surgery various systems have been proposed for registration and localization. These systems are generally similar in the methodology used and the functionality provided, with the majority of such systems employing optical trackers for the purpose of registration and localization. Typically, the vertebrae of interest is fully exposed intra-operatively, and a small number of distinct anatomical landmarks are digitized for the purpose of coarse registration. Subsequently, a larger number of points are digitized on the surface of the vertebrae to refine the registration with a surface matching technique. The procedure is often cumbersome, time consuming, and of limited accuracy. This is mainly due to difficulties in identifying characteristic anatomical landmarks in a reproducible fashion and inherent inaccuracies of surface matching techniques. While dynamic reference frames (DRFs) are commonly used to monitor target movement, any safeguarding against DRF misregistration requires the entire process, including the laborious manual digitization part to be repeated. The problem is exacerbated in procedures involving multiple vertebrae (e.g., cage placements) requiring context of percutaneous procedures, because they rely on the target structure being directly visible to the optical tracking device.
Recently, there has been some interest in fluoroscopy as an intra-operative imaging modality [1]. The relative low cost and pervasiveness of C-Arm devices in modern operating rooms (ORs) drives this interest. Most of these attempts focus on improving conventional 2D navigation techniques via tracking of the C-Arm and re-projecting pre-operative CT data onto multiple planes. Such techniques are helpful in lowering the amount of ionizing radiation delivered to the patient and the OR staff during free-hand navigation and also in providing more information to the surgeon about the relative position of the surgical tools with respect to the patient""s anatomy. However, they essentially automate and streamline the current workflow and rely on the surgeon""s ability to create a complex spatial model mentally.
Thus, there is a need for a more efficient and effective technique for performing registration and localization to track a medical instrument in an operating space that eliminates the need to establish an operating space framework and the complications associated with DRFs.
It is therefore an object of this invention to provide a technique that employs stereoscopic registration in order to relate a patient""s anatomy to pre-operative diagnostic scans in 3-D without the aid of an external calibration device.
It is another object of this invention to provide a technique that is able to track a surgical tool and localize it with respect to the patient""s anatomy and pre-operative diagnostic scans using intra-operative fluoroscopy for in situ registration.
Advantageously, the technique of the present invention does not require a fixed fiducial registration structure, nor does it require a fixed camera position relative to the operating space. Moreover, the technique provides a way of tracking a surgical tool with respect to a 3-D model, instead of using a 2-D projection.
In one aspect, the invention provides an apparatus for use in an image-guided surgical or a diagnostic procedure for tracking an instrument in an operating space that includes a target site of a patient. The apparatus comprises a data-storage medium for storing scan data representing scans of the operating space including the patient target site; an image capture device adapted to capture at least two stereo images of the operating space including the patient target site and such instrument during the image-guided surgical or diagnostic procedure; a display device; and a processor in communication with the data-storage medium, the image capture device, and the display device. The processor is operable to register selected scan data with the stereo images without using a fiducial structure, construct a composite, three-dimensional rendition showing features from the selected scan data and the stereo images, and display the composite rendition on the display device, so as to enable a user to track the instrument as it is moved within the operating space to a selected position with respect to the patient target site.
The processor preferably constructs the composite rendition using stereo photogrammetry to extract three-dimensional information from projective images, and the image capture device preferably comprises a plurality of x-ray devices adapted to capture at least two stereo radiographic images.
The apparatus is capable of tracking an instrument, which may be flexible or rigid, not visible to a user. In particular, the apparatus may be used to track a flexible instrument such as a flexible catheter through a vascular network in a patient. In such an arrangement, the data-storage medium of the apparatus stores scan data representing scans of the vascular network, and the image capture device, in the form of an x-ray device, is adapted to capture at least two stereo radiographic images of vascular network and such instrument during the image-guide surgical or diagnostic procedure. The composite rendition is displayed on the display device, so as to enable a user to track and navigate the flexible instrument as it is moved through a selected path in the vascular network to a selected position in the patient""s body.
In another aspect, the invention involves a method for use in an image-guided surgical or a diagnostic procedure for tracking an instrument, which may be flexible or rigid, in an operating space that includes a target site of a patient. The method may be used to track such an instrument whether or not it is visible to a user. The method comprises storing scan data representing scans of the operating space including the patient target site; capturing at least two stereo images of the operating space including the patient target site and such instrument during the image-guided surgical or diagnostic procedure; registering selected scan data with the stereo images without using a fiducial structure; constructing a composite, three-dimensional rendition showing features from the selected scan data and the stereo images; and displaying the composite rendition, so as to enable a user to track the instrument as it is moved within the operating space to a selected position with respect to the patient target site.
Preferably, the constructing comprises constructing the composite rendition using stereo photogrammetry to extract three-dimensional information from projective images, and the capturing comprises capturing at least two radiographic images of the operating space including the patient target site and such instrument during the surgical or diagnostic procedure.
Another aspect of the invention provides a processor-readable medium embodying a program of instructions for execution by a processor for performing a method, used in an image-guided surgical or a diagnostic procedure, for tracking an instrument in an operating space that includes a target site of a patient. The program of instructions comprises instructions for performing the above-described method.